Energy and Centrality Dependence of Chemical Freeze-out Thermodynamics parameters

TL;DR

This study investigates how chemical freeze-out parameters in heavy-ion collisions depend on collision energy and centrality, using transport and statistical models to analyze data from RHIC's Beam Energy Scan program.

Contribution

It provides a systematic analysis of chemical freeze-out parameters across energies and centralities, highlighting the saturation of temperature and the dependence on partonic interactions.

Findings

Chemical freeze-out temperature increases with energy and saturates near 10 GeV.

Baryon chemical potential decreases with increasing collision energy.

AMPT default model better describes particle yields and freeze-out parameters.

Abstract

Driven by the Beam Energy Scan (BES) program at the RHIC, researches and discussions on the QCD phase diagram have flourished recently. In order to provide a reference from microscopic transport models, we performed a systematic analysis, using a multiphase transport (AMPT) model for the particle yields and a statistical model (THERMUS) for the thermal fit, for Au+Au collisions at $\sqrt{s_{\text{NN}}}$=7.7-200 GeV. It is found that at a fixed collision centrality the chemical freeze-out parameter, temperature $T_{\text{ch}}$, increases with collision energy and somehow saturates at certain values of $T_{\text{ch}}$ in collisions near $\sqrt{s_{\text{NN}}}$=10 GeV, indicating the limiting temperature in hadronic interactions; meanwhile the baryon chemical potential $\mu_B$ decrease with the collision energy. The saturation temperature is also found to be dependent on partonic interaction. At a given collision energy, it is found that both $T_{\text{ch}}$ and $\mu_B$ decrease towards more peripheral collisions in the grand canonical approach. The energy and centrality dependence of other chemical freeze-out parameters, strangeness chemical potential $\mu_S$, strangeness undersaturation factor $\gamma_S$, and the volume of the fireball $V$ are also presented in this paper. The chemical potential ratio $\mu_s/\mu_B$ is also compared with lattice QCD calculation. The AMPT default model gives better descriptions on both the particle yields and the chemical freeze-out parameters than those from the AMPT string-melting model.